This invention is a method for making containers from multiple stacked billets. The more layers one is attempint to coextrude, the more difficult coextrusion is and more expensive the coextrusion equipment. In many typical coextrusion processes, three, five or seven layers of materials are coextruded through one coextrusion die. Oftentimes there is a barrier layer material which comprises one or more of the coextrusion layers. The barrier layer material is extremely important in that it protects the contents of the container from moisture, oxygen and other gases and from escaping aromas and flavors. Problems arise when the barrier layer contains a hole or is torn, or for some reason, is a discontinuous layer in the coextruded five, seven or nine layer sheet. A flawed barrier layer may lead to product loss or contamination. Thus, the entire extruded sheet containing the flawed barrier layer must be discarded.
To minimize this risk, it would be advantageous to have two distinct and separate sheets, each with barrier layers. In the event one of the barrier layers is flawed, the other barrier layer provides adequate protection. In this sense the container is provided with double protection by barrier layers. The present idea is to make billets of more layers by producing coextruded billets of a few layers and then stacking them in such a way that they adhere to each other and can be formed into a single product, instead of attempting to coextrude many different layers and then forming the sheet into the product.
It is simpler to make a three or five layer coextrusion than a nine layer coextrusion. In addition, it is easier to heat a thin sheet in the oven than a thick sheet. The idea of the present invention permits one to make multiple barrier layer materials from a single coextrusion line instead of necessitating two different coextrusion lines or multilayered dies. Coextrusion is also limited because it requires thick outer surface layers. The uter layers usually need to be at least 10 percent of the total layers in the extruded sheet. With the present invention, an outer layer as low as 1 percent thickness of the total layers is sufficient.